As it turns out #Gstreamer does have non-browser #WebRTC with data channels, usable from plain #CFFI even (or #C for heretics).
https://gstreamer.freedesktop.org/documentation/webrtclib/index.html?gi-language=c
That's pretty neat.
It's #Glib but... I'll take it, still much better than having to bundle a whole browser engine with whatever program I want to make interoperate with WebRTC.